They escaped and no arrests have been made, the prosecutors office said in a statement.

Sunday's attack brings the number of shooting victims in Mexico over the weekend to at least 50.

It was not immediately clear who was responsible for Sunday's attack, but the area is a key transit point for drugs heading into the US and the scene of a showdown between the Sinaloa cartel led by Joaquin 'shorty' Guzman, Mexico's most wanted man, and the Zetas gang from the country's northeast.

On Saturday, suspected cartels detonated a car bomb that killed at least four people, the first attack of its kind in Mexico's drug war, in Ciudad Juarez, another northern border city.

El Diario, a newspaper in Ciudad Juarez, said that officials from the Federal Bureau of Investigation (FBI) and other US agencies are investigating the bombing. US and Mexican officials would not comment on the allegations.

More than 26,000 people have been killed in drug violence in Mexico, mostly in the north, since Felipe Calderon, the president, took office and initiated a crackdown on drug cartels in 2006.